topic Re: create a macro in order to create an array in SAS Programming

create a macro in order to create an array

madix — Mon, 26 Mar 2018 21:36:08 GMT

Hi,

I have a question :

I would like to create a macro %array which will do the following think:

%array(y,0, n) will return for an array which length n and beginning at time t=0.

for example:

%array(x,1, n);

%array(y,0, n);

do t = 1 to n;

x_(t) = y_(t) *3+2;

y(0) = R_0 ;

do t = 1 to &H.;

y(t) = x(t)+ y(t-1);

end ;

Thank you very much for you help

Re: create a macro in order to create an array

PaigeMiller — Mon, 26 Mar 2018 21:54:27 GMT

It's not clear to me what your question is.

Re: create a macro in order to create an array

madix — Mon, 26 Mar 2018 23:10:40 GMT

I just want a macro which create an array by giving the name, the initial index number and the final one.

For example %array(z,0,n) will create an array which name is z and where I can go from z(0) to z(n).

Is it better?

Re: create a macro in order to create an array

Tom — Mon, 26 Mar 2018 23:30:52 GMT

I suspect that someone with better IML skills could show you how to do that.

But if you just want to build a matrix of literal values. Then looking at this documentation page.

http://documentation.sas.com/?docsetId=imlug&docsetTarget=imlug_workmatrix_sect004.htm&docsetVersion=14.3&locale=en

You can see that you just need make a statement like this:

y={0 1 2 3} ;

So here is a macro that could do that.

%macro array(name,start,end) ;
%local i  ;
&name = {
%do i=&start %to &end; &i %end;
};
%mend ;

If course you could also just use the simple syntax like in this help page.

http://documentation.sas.com/?docsetId=imlug&docsetTarget=imlug_workmatrix_sect014.htm&docsetVersion=14.3&locale=en

Re: create a macro in order to create an array

Rick_SAS — Tue, 27 Mar 2018 00:09:31 GMT

All arrays in the SAS/IML language are 1-based, which means that you can't use y[0].

To get started with the basics of SAS/IML, see "Ten tips for learning the SAS/IML language."

For your problem, I don't know what you are trying to accomplish, but here is some working code that you can play with to get started:

proc iml;
n=10; 
R_0 = 2;
x = j(n,   1, 0);   /* allocate (n x 1) vector; init to 0 */
y = j(n+1, 1, 0);   /* allocate (n+1 x 1) vector; init to 0 */

y[1] = R_0;         /* set first element to R_0 */
do t = 1 to n;
  x[t] = y[t]*3 + 2;
  do k = 2 to n;
     y[k] = x[k] + y[k-1];
  end;
end;

print x y;

Re: create a macro in order to create an array

madix — Tue, 27 Mar 2018 00:32:20 GMT

Thank you for your reply. I would like to do it without iml. I would like to create such a vector inside a data step. So if I use j(.,.,.) it won't work. Do you know how to do this?

Thank you very much

Re: create a macro in order to create an array

Tom — Tue, 27 Mar 2018 02:13:46 GMT

In a data step an "array" is just a convenient way to group variables. It is totally different from the real arrays and matrices that you work with in PROC IML.

What do you actually want to do. Show a small sample input dataset. Then show what you want to do. Show the resulting dataset.

A macro is just a tool to generate code. So show the code that you want to generate and explain what parts of it you need vary.

Re: create a macro in order to create an array

Rick_SAS — Tue, 27 Mar 2018 11:51:06 GMT

Since this is the SAS/IML Support Community, I assumed you wanted help with IML.

Would you like me to move this thread to the Community for DATA step programming?

Re: create a macro in order to create an array

Reeza — Tue, 27 Mar 2018 15:44:07 GMT

Does the index really matter?

SAS array statement does that by default.

So if you code:

array X(0:25) ;

You get X1-X26 because you have 26. So in this case, using an array will not save you anything unless you're trying to initialize the data. Since SAS uses an index of 1 compared to other languages, changing your index to 1 will simplify your life greatly as well.

Your macro would be:

%array(z, 0, 25);

As you can see, there's very little difference here so there's no value to a macro.

That being said, the following should be all you need, but again, it adds unnecessary complexity to your code.

%macro setUpArray(z, start, end);

array &z.(&start.:&end.) &z.&start.-&z&end.;

%mend;